The lifting capacity of an average person amounts to a few hundred pounds. For this reason, people have turned for centuries to mechanical means of lifting heavy items. Some of the means devised include pulley systems, cranes, scissor lifts, or linear actuators. One type of linear actuator of particular interest here is a rack and pinion device.
Elevators generally utilize a pulley-type system. Usually, a cable is attached to the top of an elevator box, and a counterweight is attached to the free end of the cable. The elevator box moves up and down within an elevator shaft when the cable is engaged by a motor. Safety devices are in place in the event that the cable breaks.
Though this basic system has been used for decades, there are disadvantages inherent in the pulley system method for lifting an elevator. First, the distance that an elevator can travel is limited by the length of the cable. Second, and even more importantly, the method does not maximize efficiency or cost of materials, which is desirable in the construction of green and sustainable buildings. When an elevator is lifted from the top by means of a cable, the elevator box plays an important structural role in the lifting. The box must be built for strength and stability, so that the elevator box floor is securely attached to the elevator box ceiling, where the cable is attached. On the other hand, if an elevator box were lifted from the bottom, the structure of the elevator box would be insignificant. Lighter and cheaper materials could be used to form the elevator box because the top portion of the box would not need to bear weight. In turn, the motor would not require as much power to lift the elevator if the elevator box were created from lighter materials. The machine room where the motor is stored in the case of traditional elevators could be eliminated. Furthermore, an additional structure extending the elevator shaft above the rooftop to allow access to the roof would be unnecessary. Therefore, a better elevator design would incorporate lifting from the bottom using other mechanical means.
One device that could conceptually be used for lifting an elevator from the bottom is a rack and pinion device. Rack and pinion devices are configured to convert rotational motion to linear motion. They are often used for creating horizontal linear motion, such as in transport, packaging, and assembly machines, but rack and pinion devices are also used for vertical linear motion. However, when lifting heavy items vertically, rack and pinion devices have some disadvantages. First, rack and pinion devices normally have only a few points of contact between the rack and the pinion. If a rack and a pinion have contact at only a few points, those points of contact may be put under disproportionate amounts of stress when lifting, which could cause the rack and pinion device to fail. Because reliability or safety are chief concerns in creating an elevator, taking chances with parts that might break under load could lead to disastrous results. This problem is sometimes solved by increasing the size and, therefore, the load capacity of the rack and pinion, but larger parts are harder to manufacture, require more space, and cost more. A larger rack and pinion also might require a larger motor, which further leads to decreased efficiency.
One other issue with rack and pinion devices is that these devices generally are not placed in corners. That is because the motor extending out from the pinion is generally too large to fit in the space available within the angle of the corner. This limits the versatility of the devices. In an elevator shaft, because rack and pinion devices cannot be placed in corners, they would necessarily be placed along the sides, which would limit the potential space available for access to the elevator. Furthermore, it would prevent use of the rack as part of the structure of the elevator shaft.
In light of the foregoing, what is needed is an elevator driven by a rack and chain device. A rack and chain device would allow the elevator to be lifted from the bottom, as with a rack and pinion device. However, replacing a pinion with a silent chain would allow the points of contact with the rack to be increased, taking pressure off of each individual tooth. A silent chain would also allow the motor to be distanced from the rack, so that the device could be placed in corners. However, because the profile of a typical silent chain is built to conform only to the profile of a sprocket, not a rack, a silent chain with a profile that would allow it to configure to both a sprocket and a rack, and racks and sprockets configured to engage with the silent chain, would be needed as well.